sedimentary

Chert (Jasper/Agate)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs), Color: Mottled brown, black, and tan, Luster: Waxy to vitreous, Crystal Structure: Microcrystalline/Cryptocrystalline (Trigonal), Cleavage: None (Conchoidal fracture), Specific Gravity: 2.6-2.7

Hardness: 6

Identified June 1, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the precipitation of silica from aqueous fluids or the accumulation of silica-rich organic debris (like radiolarians) on the ocean floor, subsequently undergoing lithification.

Uses & applications

Historically used for stone tools (flintknapping); currently used in jewelry as cabochons, for decorative lapidary work, and as landscaping gravel.

Geological facts

This specimen appears to be a stream-tumbled pebble. Chert is extremely durable and chemically stable, often surviving intense weathering that destroys other rock types.

Field identification & locations

Identify by its high hardness (it will scratch glass), smooth waxy texture, and shell-like (conchoidal) fracture pattern. Commonly found in riverbeds, gravel pits, and coastal areas as rounded pebbles.